Weekly images of sea surface temperature (SST) have been constructed for the tropical Atlantic Ocean for May--September, 1984--1990, from National Oceanic and Atmospheric Administration National Environmental Satellite, Data, and Information Service satellite-derived sea surface temperature data. These images have been analyzed to determine weekly to seasonal changes in the position of the fronts between the cold equatorial water and the warmer waters to the north and south. We have found that long waves along the northern front (previously reported by Legeckis and Reverdin (1987) are present each year, although their number, strength, and duration vary. The year 1987 was the most atypical, with only a few short-lived waves seen. The long waves typically appear in SST in mid-June and last into September. They form along the equatorial thermal front between 5¿W and 30¿W and propagate westward, sometimes reaching 45¿W. Wave crests travel at speeds varying between 10 and 40 cm/s, but variations in amplitude reveal that the group velocity of the waves is eastward at 30 cm/s. Long-wave crests are observed to be associated with mesoscale anticyclonic warm-core eddies, which apparently play a significant role in cross-equatorial heat transport. Instability features are also observed along the southern front of the equatorial cold tongue, although because of weaker thermal gradients they are less distinct. Southern waves propagate westward along the front at speeds and wavelengths similar to the long waves in the north. There is no simple phase relationship between long waves and the southern waves, which suggests that the southern waves are not the direct result of the northern long waves. ¿American Geophysical Union 1991